In a case where a vertical power device is formed in a SiC substrate, when an electrode for coupling the vertical power device with an electrical circuit is formed, especially, when a drain electrode is formed, it is desirable to form an ohmic electrode that reduces a contact resistance between the SiC substrate and the drain electrode.
Meanwhile, JP-A-2002-289550 discloses a method in which an ohmic electrode is obtained by irradiating a SiC substrate with a laser light. A forming process of a rear electrode using this method is performed as follows. Firstly, after an electrode is formed on a front surface side of a SiC substrate in which a vertical element is formed, a front surface of the SiC substrate is protected with a resin film, and a rear surface of the SiC substrate is thinned. Then, an ion implantation of an impurity is performed to the rear surface of the SiC substrate, and a laser light irradiation to the rear surface of the SiC substrate is performed. After that, a metal thin film is formed on the rear surface of the SiC substrate to form an electrode. Accordingly, an impurity layer that is activated by the laser light irradiation and the electrode can form an ohmic junction.
However, because it is required to perform the ion implantation of the impurity to the rear surface of the SiC substrate, there are problems that an ion implantation apparatus is expensive and an ion implantation process itself needs a high cost. Thus, it is desirable that an ohmic electrode can be obtained without the ion implantation process.
As this method, JP-A-2008-135611 suggests a method in which a laser light is emitted after a metal layer is formed on a SiC substrate. A forming process of a rear electrode using this method is performed as follows. Firstly, an electrode is formed on a front surface side of a SiC substrate in which a vertical element is formed. Next, a front surface of the SiC substrate is protected with a resin film, and the rear surface of the SiC substrate is thinned. Then, a metal layer is formed on a rear surface of the SiC substrate, and the metal layer is irradiated with a laser light. Accordingly, metal included in the metal layer and Si included in a SiC layer react to form metal silicide, thereby forming an ohmic junction.
However, it is difficult to obtain a sufficient low resistance ohmic junction only by forming the metal silicide without performing an ion implantation of an impurity, and it is desirable to obtain a lower resistance ohmic junction.